- Associated Press - Saturday, October 11, 2014

DAVENPORT, Iowa (AP) - The tunnels beneath the Davenport riverfront are big enough to drive a car into. But a car wouldn’t get far. Sections of the 80-year-old sewer culvert are so clogged with silt, the long-ago workers who walked the tunnels would have to turn back today.

From the Lindsay Park Yacht Club to a downriver area near the Davenport Sailing Club, an 11-foot-wide by 10-foot-high sewer tunnel is packed with sediment. And the U.S. Army Corps of Engineers is spending $2 million to fix it.

Engineers are confident their plan for flushing the system will work, bringing relief to long-suffering areas that can become inundated in mere measurable rainfall, the Quad-City Times reported (https://bit.ly/1sgcNNI ).

In the years before Lock & Dam 15 was built, storm and sanitary sewers discharged directly into the Mississippi River from Davenport and Bettendorf.

But the construction of the lock and dam in 1934 raised the water level in the upper pool, leading to concerns the sewers could be affected. The construction of the lock system and seawall included another component by the U.S. Army Corps of Engineers: the Government Interceptor Sewer.

Two giant tunnels were built to collect stormwater from upstream and drain it below the dam, preventing the changing water levels from inundating the sewer system. The two tunnels, dubbed the North Barrel and South Barrel, run parallel to each other for much of the Davenport riverfront and are about 20 feet underground.

In the case of the newly discovered clog, an inundation occurred at the other end of the system - from floodwater that backed into the outlet in the seawall below the dam. Corps officials said the tail water from the prolonged 2011 flood sat too long in the system, causing sediment to collect.

In 2012, when the floodwall was being built at the Iowa-American Water plant, which borders the Government Interceptor system, the clog was discovered.

“They were building the gate well, which blocks water from backing up, and they punctured a hole and realized the North Barrel was full of sediment,” said Jim Homann, project manager for the Corps’ Rock Island District. “We’re adding manholes, which we can use for future maintenance, and we have a plan for flushing out that North Barrel.”

The small maintenance building is barely noticeable among the docks and boats at the Lindsay Park Yacht Club.

But the building may hold the cure to what is ailing portions of the Government Interceptor Sewer. It contains the operations for two sluice gates, which can be opened to draw water through the seawall and into the North and South Barrels.

In work that began in August with a contract with the Corps of Engineers, workers are installing three new manholes on the Davenport riverfront.

“We’re creating access points for the sewer,” Homann said. “The workers used to walk the tunnels to inspect or repair them. The confined-spaces regulations by OSHA don’t allow that anymore.”

The project calls for seven new manholes in all, but the Corps is focusing now on three, including one on each end of the clog.

The first of the new manholes has been built on the riverfront between the Iowa-American Water plant and the Davenport Sailing Club. The mound of fill dirt that was dug from the site remains in place, awaiting the results of lab tests to determine whether it contains any hazardous debris or can simply be hauled to the landfill.

Two others are being installed at the Lindsay Park Yacht Club - one in the upriver area of the marina and the other downriver.

In the two new manholes that are farthest apart, portions of the South Barrel are being fitted with “slots.” The cutouts in the tunnel will accommodate bulkheads, which will be dropped in to create a barrier, preventing the flow of water.

“Hopefully, by diverting the water, it will clear that North Barrel,” Homann said. “The increased flow and pressure will create more force, flushing it open. When the flushing happens, that should relieve the sediment issues.”

Clogged pipes are a fact of life - in homes and under streets.

Water, sediment and other debris flow through storm sewer and sanitary sewer pipes, and backups and/or ruptures are fairly routine. They also are the reason municipalities and other public-works agencies practice routine maintenance and repair.

In Davenport and elsewhere, a big part of the problem with clogged pipes and street flooding is age. The Government Interceptor was built in 1934, and many of the city-owned lateral lines that feed into it are even older.

Given the expense, an all-out replacement of sewer lines is out of the question. So, both the city and the federal government must simply try to keep up. That is the case with the Government Interceptor Sewer, just as it is with any city project.

For instance, Davenport City Engineer Brian Schadt said, the reconstruction of River Drive in 2012 gave Public Works a clear shot at the pipes that run under it.

“During the River Drive project, the underground infrastructure was assessed,” Schadt wrote last week in an email. “At this time, it was discovered that there were some collapsed and damaged pipes. The City took advantage of the opportunity to repair these locations and install additional intake capacity in some areas.”

When crews unearthed pieces of infrastructure in the new River Heritage Park, just upriver of the Government Bridge, they found at least one manhole that was filled to the top with silt. In an area behind the LeClaire Park band shell, city crews have spent weeks investigating the source of an apparent clog that prevents rain water from properly draining.

And at the intersection of River Drive and Mound Street, a private contractor spent several days last week clearing a clog.

“As you can imagine, sediment in the pipes builds over time and becomes a periodic maintenance issue,” Schadt wrote. “The City’s Riverfront Interceptor Sanitary Sewer was scheduled for cleaning and assessment in the City of Davenport’s Capital Improvement Plan.”

Even if the pipes were crystal clear, it is unlikely some would perform perfectly.

“The cause of standing water in this area (East Village) likely is a result of the accepted design standards in place at the time the system was put in place,” he wrote.

For an 80-year-old system, the Government Interceptor Sewer is holding up well, Homann said.

“This is the first major work performed on the system since it was constructed in the 1930s,” he said. “We have no reason to think that the system will have major problems in the future.”

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Information from: Quad-City Times, https://www.qctimes.com

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